There is an existing coil component as disclosed in Japanese Unexamined Patent Application Publication No. 11-97249. The coil component includes a toroidal core and a first coil and a second coil wound around the toroidal core.
In the above-described existing coil component, when a normal mode current flows through the first coil and the second coil, a first magnetic flux by the first coil and a second magnetic flux by the second coil are generated in the toroidal core. The first magnetic flux and the second magnetic flux are in reverse directions, so that the first magnetic flux and the second magnetic flux cancel each other. Therefore, normal mode impedance cannot be increased. When the number of turns of the first coil or the second coil is increased, the normal mode impedance is increased but common mode impedance is also increased.